In biochemical assays for nucleic acids, proteins and the like, particulate carriers called “microbeads” have been used. For example, in assays of nucleic acids, there are used microbeads wherein a probe nucleic acid chain having a complementary base sequence relative to a target nucleic acid chain is solid-phased on a surface thereof. The target nucleic acid chain is isolated based on the interaction between the target nucleic acid chain and the probe nucleic acid chain. In protein assays, microbeads, on which an antibody relative to a target protein is solid-phased on a surface thereof, are used to isolate the target protein in a similar way.
In the biochemical assays making use of these microbeads, a higher throughput has been recently demanded, for which there are being developed techniques of realizing high-speed assays.
In Patent Document 1, for example, there is disclosed “A method for detecting analytes among a number of analytes in a sample, the first-mentioned analytes being recognized with the respective analytical reactants, the method including: (a) bringing, into contact with a sample, a number of populations of fluorescent particles, which populations, respectively, have different fluorescent signals and different analytical reactants wherein the analytical reactant specifically binds to one analyte in the sample and each fluorescent particle has, on a surface thereof, at least one nanoparticle labeled with each corresponding fluorescent dye, (b) adding a labeling reagent to the sample, (c) detecting the label to analyse the fluorescent particle indicating the binding of the analytical reactant with the analyte, and (d) simultaneously determining the populations of the fluorescent particles bound to the respective analytes from the function of the different fluorescent signals associated with the respective populations”.
In “Suspension Array Technology” provided by Luminex Trading, Inc., based on this technique, two types of fluorescent dyes are labeled on a microbead while imparting a change in emission color, thereby enabling 100 types of microbeads in maximum to be discriminated from one another. According to the “Suspension Array Technology,” when different probe nucleic acid chains and antibodies are, respectively, solid-phased on 100 types of microbeads, it becomes possible to simultaneously isolate and detect 100 different types of nucleic acid chains and proteins through one assay.
In the above document, it is recited that “the populations of the fluorescent particles are further determined depending on the sizes and shapes thereof” and it is disclosed that for the additional parameters of discriminating microbeads, the size and shape of the bead can be adopted (see Paragraphs 0037 and the like of the document). Further to this, in Non-Patent Document 1, there is described a method of making a number of differently shaped microbeads according to photolithography in a flow path. According to this method, fabrication of greater than one million types of microbeads becomes possible.    Patent Document 1: Japanese Patent Publication No. 3468750